The procedures for determining the flexibility of vehicle paints are described in the "Toyota TSH1504G Test method for flexibility of paint film" standard developed by the Toyota vehicle company.
In assessing the properties of the paint film, elasticity is a very important indicator that reflects the elasticity, plasticity and adhesion of the film under the influence of external forces. Flexibility testing helps understand whether the coating can maintain its integrity and performance during actual use, as well as its response to external shocks.
Flexibility tests generally used in coating film evaluation include two common methods:
The flexibility tester used in the first method uses a series of steel spindle rods of different thicknesses to check whether the film cracks by bending it 180 degrees. Spindle rods of different diameters such as 180mm, 1mm, 2mm, 3mm, 4mm, 5mm and 10mm are used for 15 degree bending during testing. The minimum rod diameter without film breakage is used to indicate the flexibility of the film.
This testing method takes into account the elasticity, plasticity and adhesion of the film to the substrate. Test results are also affected by factors such as deformation time and speed. However, although this method allows the evaluation of the flexibility of the film, shaft rods of different diameters may cause interruptions in the test results.
The second method uses a cone bending tester. To avoid the discontinuity of test results caused by different coaxial rod diameters, the conical bending tester becomes another type of flexibility tester. This device is specially designed to test the bending properties and bending strength of materials. It consists of a tapered shaft made of high-quality stainless steel, resistant to wear and corrosion. The size of the cone shaft is 3,1 mm in diameter at the small end, 38 mm in diameter at the large end and 203 mm in length.
During this test, the sample is placed on the cone axis of the cone bending machine and force is applied, causing the sample to bend and deform. By measuring the applied force and the deformation of the sample, the bending properties and bending strength of the material can be determined. This method is simple and easy to use and is suitable for testing the bending properties of various materials.
Essentially, flexibility testing plays an important role in film evaluation. The flexibility of the film determines its response to external forces and whether it can prevent cracking and falling off. This is directly related to the lifespan, maintenance cycle and appearance quality of the film. Thanks to the flexibility test, the performance of the film under different stress conditions is understood, which provides an important basis for the selection and application of the film.
The flexibility of the paint film is one of the important indexes to evaluate its performance. Flexibility testing helps understand the performance of the film in actual use by evaluating the flexibility, plasticity and adhesion of the film under external force. 180 degree bending test of steel shaft bar and cone bending tester test are common flexibility testing methods that provide different viewing angles to evaluate the performance of the film. These test methods provide valuable information for film selection, application and maintenance.
Briefly, flexibility tests are used to determine a coating's elongation and resistance to cracking. Bending and impact tests used to evaluate the flexibility of coatings detect deformation resulting from bending and impact. Deformation is distinguished into two types according to the flexibility of the coating on a substrate:
Generally, different testing methods used to test the flexibility and durability of coatings include mandrel bending test, impact strength test and cupping test.
Mandrel testing is used to determine the resistance of coatings to cracking after bending after application and curing on sheet metal or other flexible materials. Impact tests determine the toughness or impact resistance of a coating to absorb energy under mechanical load. Cupping tests are designed to test the elongation and deformability of polishes and protective coatings applied to metal surfaces. In this test, a coated sheet is subjected to gradual deformation with a polished die. This deformation is caused by the mold being pushed from under the coating, i.e. from the back side of the sheet. The final point is when the coating begins to crack.
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